I also would go with a 75g tank over the 55g first off. Better footprint for aquascaping and more fish possibilities.
I'd start with a a sump/refugium like this
Eshopps Refugium R-100, 75-125g, 2nd Generation - AquaCave
Then I'd get an octopus skimmer, not sure which one but it would be a good one.
Protein Skimmer, Protein Skimmers, Aquarium Marine Reef Foam Fractionators
For flow i would go with 2 of these Vortech MP10W ES Propeller Pump by EcoTech Marine - AquaCave
For lighting I would go with this
Aqua Illumination LED Aquarium Lighting
Hmmm what else....I would get a controller too and an ATO
Reef Keeper ELITE V2 System by Digital Aquatics - AquaCave
JBJ ATO Automatic Top Off System Water Level Controller - AquaCave
I'd have a deep sand bed and about 150 lbs of rock.
theres also the list of doodads that would be good to have : An ro
unit for water making, a refractometer for salinity and top of the line test kits. lol
Just an off the top of my head list.
theres ALWAYS something else you'll run into that you'll want. I'd also love to have a dosing pump setup as well since I have a good amount of corals.